Theoretical Study on Transient Hot-Strip Method by Numerical Analysis

Abstract

This paper presented the effects of finite dimensions of the sample and nonzero heat capacity of the strip on thermal conductivity determination with the transient hot-strip method. Through the numerical analysis of the temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared with the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have a great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity is always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated to be less than 2.1% for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120×60 mm2(width×thickness) and the fitting time interval of 20–300 s. The nonzero heat capacity of the strip has a great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated to be less than 5% for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip.